Photoelectric conversion device, radiation detection apparatus, image processing system and driving method thereof

ABSTRACT

In a photoelectric conversion device, in order to suppress alteration of its properties during a long time use, lower the decrease of the S/N ratio due to a dark current output, and shorten image-pickup cycles, MIS type photoelectric conversion elements using an amorphous semiconductor material are connected with an electric power source for applying bias for photoelectric conversion, an electric power for resetting an accumulated electric charge, and a setting point for applying zero bias at the time of non-operation of the element through a switch. Emitted x-rays from an x-ray source, which is a first light source, come into collision against phosphor after being transmitted through an object body to be inspected and then are absorbed in the phosphor to be converted into visible light rays. The visible light rays from the phosphor are radiated to the photoelectric conversion elements. Prior to reading out of the x-ray image, an LED light source is lighted. Switches are used for turning on the x-ray source and the LED light source. In this embodiment, there is a reading-out period and a non-reading-out period; the x-ray source is turned on during the reading-out period, and the LED light source is turned on during the non-reading-out period.

This application is a division of application Ser. No. 09/911,616, filedJul. 25, 2001, the contents of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a photoelectric conversion device,particularly, a photoelectric conversion device for office appliancessuch as a copying machine, a facsimile, a scanner, or the like and aphotoelectric conversion device to be used for an x-ray camera tubeapparatus for medical use to be used for diagnosis or to be used fornondestructive inspection apparatus; an image processing (imageinformation or image data processing) system; and their driving method.

2. Related Background Art

Conventionally, x-ray direct radiography has been carried out by aso-called film way, which has been a mainstream method carried out byradiating x-rays to a patient and transferring the transmitted x-rays toa photosensitive film through visible light conversion phosphors. Thefilm way has problems that it takes a long time from photographing todeveloping processes and that it requires to store and search an immensenumber of photographed films in terms of maintenance and management in ahospital.

By the way, there is another way available using extremely brightphosphors in place of the film which is carried out by storing an x-rayimage of a patient in the extremely bright phosphors, scanning the imagewith a laser beam thereafter, and reading the x-ray image as digitalvalues. If an image is converted to be digital, that makes recording ina variety of media possible, so that image storage, search, and transfercan easily be carried out to improve the efficiency in a hospital interms of the maintenance and management. Further, obtaining image dataas digital values makes highly advanced image processing by a computerpossible and is expected to result in improvement of diagnosis.

However, even the way using extremely bright phosphors has, as in thefilm way, a problem that it takes a long time from photographing todeveloping.

On the other hand, an x-ray imaging apparatus using a solid imaging(image-pickup) device such as CCD and an amorphous silicon semiconductorhas been proposed. As in the film way, it is carried out by directlyconverting an x-ray image of a patient obtained through visibleconversion type phosphors by x-ray radiation to a digital image,approximately in real time, by a large number of imaging (image-pickup)elements arranged in a two-dimensional array and reading the image.Since the digital image can be obtained approximately in real time, ascompared with the above described film way and the way using theextremely bright phosphors, it is greatly advantageous. Especially,since amorphous silicon can be formed in a large surface area, in thecase of an x-ray imaging apparatus using such amorphous silicon,photographing (image-pickup) of a large portion such as chestphotography can be carried out in equal size. Consequently, a high lightutilization factor is provided and a high S/N ratio is expected.

However, in an x-ray imaging apparatus for medical use, in order tophotograph a chest of a human being in equal size, it is required tomake available a solid imaging device with a large surface area as wideas 40 cm×40 cm and a number of pixels as extremely high as 5,000,000 to10,000,000.

It is not so easy to produce the properties of these immense numbers ofpixels all evenly and reliably. For example, in the case of usingamorphous silicon for photoelectric conversion elements and switchingelements for charge transfer, if continuous operation is carried out fora long duration, dark current of the photoelectric conversion elementswill be increased and the properties of the switching elements will bechanged. To deal with such cases, a countermeasure employed is that thephotoelectric conversion elements and the switching elements are sodesigned as to be operated only at the time of taking images and so asto be inhibited from operation at the time of taking no image. Forexample, when no patient is in a photographing chamber, bias wires ofthe photoelectric conversion elements and gate wires and reading-outwires of the switching elements are biased to be at zero potential, andno electric field is applied to the insides of the amorphous elements tolower the property alteration of the elements in a long time use.However, this case has a complicated handling of operating thephotoelectric conversion elements and switching elements afterrecognizing the presence of a patient near the imaging apparatus andthen carrying out an image pickup operation. In other words, operabilityof the apparatus is deteriorated. A design to automatically recognizethe existence of a patient may also be possible; however, it leads to anincrease in cost of an apparatus.

On the other hand, in the case where a large number of photoelectricconversion elements with a large surface area is fabricated using anamorphous silicon thin film, there are problems that traces ofimpurities are mixed in fabrication processes and dangling bonds tend tobe increased and that they form as defect levels. They work as trappinglevels and become unnecessary dark current in the photoelectricconversion process to decrease the S/N ratio. As a driving method of aphotoelectric conversion device in which the dark current is lessened,possible is a method of carrying out photoelectric conversion after thedark current is moderated by waiting for several to several 10 secondsfrom biasing the photoelectric conversion elements (and switchingelements). However, if such a method is employed for an x-ray imagingapparatus, the cycle for taking images of a plurality of patients willbecome long.

As described above, in the photoelectric conversion device with a largesurface area using amorphous silicon, it is made difficult to keep ahigh S/N ratio owing to the property alteration during a long time useand defect levels in a film and hence, a photoelectric conversion deviceand its driving method capable of being operated easily while keepinggood S/N ratio have been expected to be developed.

SUMMARY OF THE INVENTION

An object of the present invention is to lower the property alterationduring a long time use and the S/N ratio owing to dark current, shortenthe imaging (image-pickup) cycles, and improve the operability of aphotoelectric conversion device, an image data processing system andtheir driving method.

A photoelectric conversion device of the present invention in accordancewith the above described objects is a photoelectric conversion devicecomprising: a photoelectric conversion substrate comprising a substrateand a plurality of photoelectric conversion elements arranged on thesubstrate; a light source; and an outer casing for housing thesemembers, wherein, between a reading-out period for obtaining image data(image information) and a non-reading-out period in which reading-out isnot carried out, the light source is turned on in the non-reading-outperiod.

Also, the present invention provides a photoelectric conversion devicecomprising a substrate equipped with a plurality of photoelectricconversion elements for photoelectrically converting incident light rayshaving the image data and light sources for radiating light rays havingthe foregoing image data and light rays having no image data to aplurality of the foregoing photoelectric conversion elements.

Further, the present invention provides an image data processing systemcomprising: a photoelectric conversion device comprising a substrateequipped with a plurality of photoelectric conversion elements forphotoelectric conversion of incident light rays having the image dataand a light source for radiating light rays bearing no image data to aplurality of the foregoing photoelectric conversion elements, aradiation source, and control means for independently controlling theforegoing radiation source and the foregoing photoelectric conversiondevice.

Further, the present invention provides an driving method of an imaging(image-pickup) apparatus, comprising first and second light sources anda semiconductor element comprising a semiconductor layer having anabsorption region of the wavelength of the light rays radiated from theforegoing second light source, wherein the image data is read out byradiating light from the foregoing first light sources during theimaging (image-pickup) period and radiation by the foregoing secondlight sources is carried out during the non-imaging period.

Furthermore, the present invention provides a radiation detectionapparatus comprising: a photoelectric conversion substrate comprisingphotoelectric conversion elements arranged on a substrate and an outercasing for housing the photoelectric conversion substrate, wherein theradiation detection apparatus is further provided with a light source inthe outer casing and is further provided with a wavelength converter forreflecting the light rays from the light source and entering thereflected rays in the foregoing photoelectric conversion elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a photoelectric conversion device ofEmbodiment 1 of the present invention;

FIG. 2 is a diagram of a circuit using a photoelectric conversionelement of Embodiment 1 of the present invention;

FIG. 3 is a timing chart (1) of the circuit illustrated in FIG. 2;

FIG. 4 is a timing chart (2) of the circuit illustrated in FIG. 2;

FIG. 5 is a timing chart (3) of the circuit illustrated in FIG. 2;

FIG. 6 is a plan view of a photoelectric conversion element and aswitching element shown in FIG. 1;

FIG. 7 is a cross-sectional view taken along the line 7-7 of FIG. 6;

FIG. 8 is a diagram of a two-dimensional electric circuit of thephotoelectric conversion device shown in FIG. 1;

FIGS. 9A, 9B and 9C are band diagrams showing an operation of an MIStype photoelectric conversion element shown in FIG. 1;

FIG. 10 is a timing chart showing an operation of FIG. 8;

FIG. 11 is a cross-sectional view of a photoelectric conversion deviceof Embodiment 2 of the present invention;

FIG. 12 is a cross-sectional view of a photoelectric conversion deviceof Embodiment 3 of the present invention;

FIG. 13 is a cross-sectional view of a photoelectric conversion deviceof Embodiment 4 of the present invention;

FIG. 14 is a cross-sectional view of a photoelectric conversion deviceof Embodiment 5 of the present invention;

FIG. 15 is a cross-sectional view of a photoelectric conversion elementof Embodiment 6 of the present invention;

FIG. 16 is a timing chart (1) of the circuit illustrated in FIG. 15;

FIG. 17 is a timing chart (2) of the circuit illustrated in FIG. 15;

FIG. 18 is a timing chart (3) of the circuit illustrated in FIG. 15; and

FIG. 19 is a block diagram of a photoelectric conversion device ofEmbodiment 7 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be describedaccording to the drawings. The radiation used in the present inventionincludes x-rays, γ-rays, α-rays, β-rays, and the like.

(Embodiment 1)

FIG. 1 is a cross-sectional view of Embodiment 1 of a photoelectricconversion device according to the present invention. In the drawing,reference numeral 101 denotes a light ray source, 102 an object body tobe read out, 103 a chassis, 104 a phosphor, 105 a photoelectricconversion element, 106 an insulating substrate, 107 a protective layer,and 108 an LED. This embodiment is performed by employing aphotoelectric conversion device of the present invention for a radiationdetection apparatus, especially, an x-ray imaging (image-pickup)apparatus.

In FIG. 1, the x-rays emitted out from the x-ray source 101 are radiatedto the object body to be read out 102; the x-rays transmitted throughthe object body to be read out 102 reach the phosphors 104 and areconverted into visible light rays by the phosphors 104. The visiblelight rays from the phosphors 104 are photoelectrically converted inlight-receiving faces of photoelectric conversion elements 105 arrangedon an insulating substrate 106. The photoelectric conversion elements105 are covered with the protective film 107 for the purpose ofimproving moisture resistance.

As the materials for the insulating substrate 106, usable is mainlytransparent glass with a little amount of alkaline components. Theinsulating substrate may be made of a plurality of insulating platesstuck to each other. Further, as the wavelength converter, phosphors aresuitable to be used and as the materials for the phosphors, usable areGd₂O₂S:Tb, CsI:Tl or the like.

On the other hand, the light rays (visible light rays) emitted from theLED 108 installed under the insulating substrate 106 are transmittedthrough the insulating substrate 106 and after passing the side faces ofthe photoelectric conversion elements 105, the light rays are reflectedby the phosphors 104 and radiated to the light-receiving faces of thephotoelectric conversion elements 105. The phosphors 104 have differentreflecting characteristics of light rays from the LED 108 depending onthe materials; however, any can be used unless the phosphors completelyabsorb light rays, and any that emits light rays of several % to thephotoelectric conversion elements 105 may be usable.

In FIG. 1, the illustration is drawn as if the light rays from the LED108 are perpendicularly radiated to the phosphors 104; however, somelight rays enter from a diagonal direction and therefore, it is supposedthat there are some components reflected by the phosphors 104 if thosereflected by the mirror faces of the phosphor faces are included in thecomponents.

In FIG. 1, the photoelectric conversion device of the present embodimentcomprises the phosphors, the photoelectric conversion elements, LEDs orthe like housed in an outer casing such as a chassis. The outer casingmay be made of a material with extremely low x-ray absorption in theincident surface of x-rays, and metals such as aluminum, a stainlesssteel or the like are suitable to be used owing to the economical costand the high strength.

If the x-ray imaging apparatus employing the above describedphotoelectric conversion device is for a medical use, the object body tobe read out is a patient (human body) and if the x-ray imaging apparatusis for non-destructive inspection, the object body to be inspected maybe parts used for, for example, aircrafts and ships.

Further, FIG. 1 shows a cross-sectional view of the photoelectricconversion device, in which the photoelectric conversion elements andLEDs are arranged in two dimensions in the depth direction of thesurface of FIG. 1. Further, although omitted in FIG. 1, switchingelements may be arranged while being coupled with the photoelectricconversion elements in pairs on the insulating substrate.

FIG. 2 is a diagram of a signal detection circuit of a singlephotoelectric conversion element to be employed for the photoelectricconversion device illustrated in FIG. 1. In the figure, the referencenumeral 201 denotes an x-ray source, 202 a phosphor, 203 a photoelectricconversion element, and 204 an LED light source.

In FIG. 2, the photoelectric conversion element 203 is an MIS typephotoelectric conversion element using an amorphous siliconsemiconductor as a material. The MIS type photoelectric conversionelement is constituted by stacking an insulating layer (insulator) and asemiconductor layer (semiconductor) on a lower part metal electrodelayer (metal). Generally, an injection element layer (an n-type layer ora p-type layer) and an upper part electrode are arranged on thesemiconductor layer. A detailed fabrication method and the operationprinciple of the MIS type photoelectric conversion element will bedescribed later.

In FIG. 2, a power source for applying bias (Vs) for photoelectricconversion, a power source (VREF) for resetting accumulated charges inthe capacity of the MIS type photoelectric conversion element, and aground point (GND) for applying zero bias (VGND) when no photoelectricconversion element is operated are connected to the MIS typephotoelectric conversion element through SW1.

The x-rays emitted from the x-ray source 201 which is a first lightsource are radiated to an object body, which is not illustrated in FIG.2 (a patient in the case of a hospital), and the transmitted x-rayscollide with a wavelength converter.

In FIG. 2, the x-rays are converted into visible light rays by thephosphor 202 which is a wavelength converter. The visible light raysfrom the phosphor 202 are radiated to photoelectric conversion element203. FIG. 2 shows an illustration only for one pixel, and thepositioning correlation between the photoelectric conversion element 203and the phosphor 202 is therefore not illustrated; however, as may beunderstood from FIG. 1, the image resolution property is improved bypractically closely sticking both of them to each other. On the otherhand, the visible light rays from the LED light source 204, which is asecond light source, are radiated to the photoelectric conversionelement 203 through another optical path different from the path for thex-rays. SW2 and SW3 are switches for turning on the x-ray source 201 andthe LED light source 204, respectively.

FIG. 3 is a timing chart of operation in the circuit shown in FIG. 2 andshows the x-ray source, the LED light source, bias of the photoelectricconversion element, and the output of the photoelectric conversionelement.

In FIG. 3, the x-ray source and the LED are not turned on in order toshow the state of dark output (dark current) of the photoelectricconversion element. FIG. 3 shows the time chart of 6 cycles of (F1) to(F6).

In the cycle (F1), when bias potential is applied to the photoelectricconversion element, the dark current flows. Ideally, it is preferablefor the dark current to be zero; however, it is difficult to keep itzero. Further, a constant electric current does not flow simultaneouslywith the time when the electric power source is turned on, but it ishigh immediately after the turning on and gradually decays with thelapse of time.

As this cause, the following two are considered.

One is that in the case where photoelectric conversion elements arefabricated using an amorphous silicon semiconductor as a main material,defect levels are generally formed by dangling bonds in the amorphoussemiconductor film and impurities mixed in the fabrication process. Theywork as trap levels and immediately after the electric power source isturned on or even before the source is turned on, they trap electrons orholes and are thermally excited to a conduction band or a valence bandafter several milliseconds to several ten seconds and thus conductioncurrent (dark current) flows. It is said that many trap levels exist,especially in the interface portion between a semiconductor layer (ani-type layer) and an injection inhibiting layer (for example an n-typelayer). In the case where crystal type MIS photoelectric conversionelements are employed without using amorphous semiconductor films, it issaid that the trap levels are not so many as those in the case of usingamorphous semiconductor films, although they depend on the fabricationprocess conditions and the apparatus to be fabricated. However,mismatches of crystal lattices are many in the interface portion betweenthe semiconductor layer (an i-type layer) and the injection inhibitinglayer (for example an n-type layer), and the trap level is not at zero.The photoelectric conversion elements tend to have an output of aphotoelectric conversion element shown in FIG. 3.

The other cause is considered to be relevant to the property of theinjection inhibiting layer. For example, in the case where the injectioninhibiting layer is made of an n-type amorphous silicon, theoretically,holes are not injected to the semiconductor layer side. However,actually, particularly in the case of an amorphous layer, the n-typelayer cannot completely block the holes. The holes injected to thesemiconductor layer (i-type layer) through the n-type layer become darkcurrent. The holes are accumulated in the interface between thesemiconductor layer (i-type layer) and the insulating layer, and aninternal electric field in the i-type layer is moderated along with theaccumulation of the holes. Following the moderation of the electricfield, the quantity of the holes injected from the n-type layer to thei-type layer is decreased, and therefore the dark current is decayed.

Signals with high S/N ratio can be obtained by waiting until the darkoutput of the photoelectric conversion elements shown in FIG. 3 issufficiently decayed. However, it takes a long time, from severalseconds to several ten seconds, until the dark output is decayed to anaiming level. In this case, for example, when the photoelectricconversion elements are employed for an x-ray imaging apparatus to beused in a hospital, the following procedure is required: a patient isguided to a photographing chamber, the photoelectric conversion elementsare turned on, and after waiting for several to several ten seconds, thepatient is subjected to x-ray exposure.

It is better to turn on the photoelectric conversion elements before apatient comes in the photographing chamber; however, in that case,deterioration (property change, corrosion, or the like) of thephotoelectric conversion elements is accelerated, making it difficult toprovide an apparatus with a long life.

In an MIS type photoelectric conversion element, no electron and no holepasses the internal insulating layer, and the generated carriers areaccumulated in the interface between the semiconductor layer and theinsulating layer. In the case where the bias (Vs) for photoelectricconversion shown in FIG. 2 is plus (+) bias, the accumulated carriersare holes and an n-type layer for inhibiting injection of the holes intothe semiconductor layer is formed between the upper part electrode andthe semiconductor layer. Electrons in equal quantity of the holecarriers accumulated in the interface between the semiconductor layerand the insulating layer are supplied from the GND to the electrode sidewhere an ammeter is installed. The accumulated holes are either entirelyor partially swept by controlling the bias of the sensor to VREF in ashort time. Generally, the potential of the VREF is set lower than thepotential of the VS. In the timing chart of FIG. 3, the potential ofVREF is set to be the GND. In the cycle (F2), by applying the potentialVS again, dark current similar to that in the cycle (F1) flows.

At that time, the dark current becomes low as compared with that in thecycle (F1). That is supposedly attributed to that carriers relevant tothe dark current and collected in the trap levels existing in the i-typelayer, especially in the periphery of the interface to the insulatinglayer, are lessened more in the cycle (F2) than in the cycle (F1).Further, it is also supposedly attributed to that the holes accumulatedby the reset potential VREF of the cycle (F1) are not completelyexpelled and some remain in the semiconductor layer to consequentlymoderate the electric field in the inside of the semiconductor more inthe cycle (F2) than in the cycle (F1).

In the same manner, as the cycles proceed from the cycle (F3) to thecycle (F6), the dark current is lowered and soon saturated.Nevertheless, although saturation takes place, since rush current flowsat the time of switching the bias from the VREF to VS, the current valuedoes not become a constant current value immediately after theswitching. In the latter half, even in one cycle, especially,immediately before switching to VREF, the current becomes constantwithout change with the lapse of time. In order to surely keep as highan S/N ratio as an x-ray imaging apparatus, it is preferable that x-raysare radiated after the dark current is sufficiently reduced.

FIG. 4 is a timing chart obtained by radiating x-rays in the cycle (F6)after taking sufficient time. Since the properties of dark current inthe cycle (F5) and in the cycle (F6) are approximately the same, thesteady part overlaid on the current output by the x-rays in the cycle(F6) can easily be corrected by storing the output of the cycle (F5) ina memory and then subjecting the subtraction processing thereafter.Incidentally, the output of the cycle (F7), which is not illustrated inFIG. 4, may be used.

Although depending on the properties of the dark current of thephotoelectric conversion elements and the operation conditions of theapparatus, the period of each cycle of (F1) to (F6) takes generally 0.1to 3 seconds. Supposing it is 2 second/cycle, it takes 12 seconds for 6cycles. In other words, from the time when bias is turned on, it takes10 seconds or more until x-ray photographing is carried out.

FIG. 5 is a timing chart obtained in the case of radiating x-rays andlight rays from a light source.

During two operation periods, a reading-out period and a non-reading-outperiod, a first light source is turned on during the reading-out period,and a second light source is turned on during the non-reading outperiod. In the case of an x-ray imaging apparatus for medical use, thefirst light source is an x-ray source. In the case of a nondestructiveinspection apparatus, the first light source is x-rays or another typeof radiation. On the other hand, the second light source may be LED(light emitting diodes) and EL (electroluminescence), and any lightsource may be used as long as it has an electroluminescence wavelengthin the wavelength region of light absorption of the photoelectricconversion elements.

The x-rays from the first light source, which is not illustrated, arethe light rays to be radiated to an object to be photographed in orderto obtain image data of the object (the object to be photographed). Thelight rays from the second light source are not necessary to be radiatedto the object (the object to be photographed) and it is sufficient forthe light rays to reach the photoelectric conversion elements throughany optical path.

In FIG. 5, the LED (the second light source) is turned on in the cycle(F2) and the x-ray source (the first light source) is turned on in thecycle (F3). In the example shown in FIG. 5, the cycle (F1) and the cycle(F2) are the non-reading-out period and the cycle (F3) is thereading-out period.

The photocurrent flowing owing to the light radiation by the LED is notread as an image signal. That is, the LED is lighted during thenon-reading-out period, the cycle (F2).

Although the photocurrent flows owing to the light radiation by the LED,simultaneously with the turning-off of the light, the state that darkcurrent is flowing can be restored. However, after the LED is turnedoff, as shown in FIG. 5, lower and more stabilized dark output (darkcurrent) flows than the dark output (the dashed line) of the case wherelight rays of the LED are not radiated in the cycle (F2).

That is attributed to that the photo energy of the LED is absorbed inthe semiconductor layer, the generated carriers are accumulated in theinterface with the insulating layer, the inner electric field in thesemiconductor layer is moderated, and the carriers flowing therein fromthe injection inhibiting layer are consequently decreased. In the nextcycle (F3), as shown in FIG. 5, since the generated carriers by the LEDlight rays of the cycle (F2) cause effects of operating several cyclesin a dark state, the dark current is in a stable state. Further, it isalso possible to be supposed that the previously trapped electrons orholes relevant to the dark current are decreased by the light radiation.

If x-rays are radiated in such a low dark current state, signals with ahigh S/N ratio can be obtained.

In other words, if the dark current is lowered by radiating LED lightrays before x-ray image-pickup (photographing), an x-ray image with ahigh S/N ratio can be obtained without requiring a long time to wait.

The radiation duration and the intensity of the light rays in the cycle(F3) in FIG. 5 are optional as long as they lower the dark current andmay be, for example, approximately the dark current after the cycle (F6)in FIG. 3. By radiating x-rays in the cycle (F3) of the reading-outperiod, signals with a high S/N ratio can be obtained. Although it isnot illustrated in the figure, if the signals of the cycle (F4) aretaken in and subtracted from the x-ray outputs of the cycle (F3), thefixed components in the dark current contained in the x-ray signals ofthe cycle (F3) can be corrected. As a result, if the dark current islowered by radiating LED light rays before x-ray photographing, an x-rayimage with a high S/N ratio can be obtained without requiring a longtime to wait.

Although FIG. 5 is a timing chart where the cycle (F1) and the cycle(F2) are set to be the non-reading-out periods and the cycle (F3) is setto be the reading-out period, of course, it is also possible to radiatelight rays by LED, which is the second light source, during thenon-reading-out period in the cycle (F1) and to set the cycle (F2) to bethe reading-out period. In that case, the time up to the x-ray radiationcan further be shortened.

FIG. 6 shows the plan view of a photoelectric conversion substrateconstituted using amorphous silicon semiconductor thin films for thephotoelectric conversion elements and switching elements arranged on aninsulating substrate shown in FIG. 1, and the wirings bonding theseelements are also illustrated together. FIG. 7 shows the cross-sectionalview taken along the line 7-7 shown in FIG. 6.

In FIG. 6 and FIG. 7, the photoelectric conversion elements 601 and theswitching elements 602 (amorphous silicon TFT, hereinafter referred asto “TFT”) are formed on the same photoelectric conversion substrate(insulating substrate) 603. The lower part electrode which is the firstelectrode layer of the photoelectric conversion element 601 and thelower part electrode (gate electrode) of the TFT 602 are commonly madeof the same first metal thin film layer 604. The upper part electrodewhich is the second electrode layer of the photoelectric conversionelement 601 and the upper part electrode (source electrode and drainelectrode) of the TFT 602 are commonly made of the same second thin filmlayer 605. Further, the first and the second metal thin film layers usedfor the electrode layers 604 and 605, respectively, are commonly usedfor the wiring 606 for gate operation and the matrix signal wiring 607of the photoelectric conversion circuit, respectively.

In FIG. 6, the number of pixels is 2×2, 4 pixels in total. The hatchingpart shown in FIG. 6 is light-receiving faces of the photoelectricconversion elements 601. The reference numeral 609 denotes a powersource line to apply bias to the photoelectric conversion elements.Further, the reference numeral 610 denotes a contact hole to connect aphotoelectric conversion element 601 and the TFT 602. The light raysfrom the light source installed under the photoelectric conversionsubstrate 603 are led to the side of the phosphor 616 in the surroundingof the photoelectric conversion elements 601 from a region where thefirst metal thin film layer 604 and the second metal thin film layer 605do not exist. Light rays are shielded by the first metal thin film layer604 immediately under the photoelectric conversion element 601.

Next, the fabrication method for fabricating a circuit part of aphotoelectric conversion device of this embodiment will be described.

FIG. 7 is a cross-sectional view taken along the line 7-7 shown in FIG.6 showing the plan view of the photoelectric conversion substrate.

In FIG. 7, chromium (Cr) is deposited in a thickness of 50 nm as a firstmetal thin film layer 604 on an insulating substrate 603 by a sputteringmethod and a resistance heating method and patterned byphotolithographic patterning, and the unnecessary areas are removed byetching. The first metal thin film layer 604 becomes a lower partelectrode of a photoelectric conversion element 601 and a gate electrodeof a switching element 602. Next, an a-SiN_(x) layer (611), an a-Si:Hlayer (612) and an n⁺-layer (613) are successively formed in 300 nm, 500nm, and 100 nm film thickness, respectively, in the same vacuumatmosphere by a CVD method. The respective layers 611 to 613 arerespectively an insulating layer, a photoelectric conversionsemiconductor layer, and a hole injection inhibiting layer of aphotoelectric conversion element 601 and respectively become a gateinsulating film, a semiconductor layer, and an ohmic contact layer of aswitching element 602 (TFT). They are also used as an insulating layerin a crossing part (614 in FIG. 6) of the first metal thin film layer604 and the second metal thin film layer 605. The film thickness of eachof the layers 611 to 613 is not restricted to the above describedthicknesses and may be properly designed depending on the voltage andthe electric charge employed for a photoelectric conversion device andthe incident light intensity of the light-receiving faces of thephotoelectric conversion elements. At least, the thickness of thea-SiN_(x) layer 611 is preferably 50 nm or more so as to inhibit bothelectrons and holes from passing through and sufficiently function as agate insulating film of a TFT.

After the respective layers 611 to 613 are deposited, areas which becomecontact holes (610 in FIG. 6) are dry-etched by RIE, CDE or the like andafter that, aluminum (Al) as the second metal thin film layer 605 isdeposited in about 1,000 nm by a sputtering method or a resistanceheating method. Further, patterning is carried out by photolithographyand the unnecessary areas are removed by etching. The second metal thinfilm layer 605 becomes an upper part electrode of a photoelectricconversion element 601 and a source electrode and a drain electrode of aswitching TFT 602 and other wirings. Further, simultaneously with thefilm formation of the second metal thin film layer 605, the upper andthe lower metal thin films are connected through the contact hole parts610. Further, in order to form a channel part of the TFT 602, a partbetween the source electrode and the drain electrode is etched by RIEmethod and after that unnecessary parts of the a-SiN_(x) layer, thea-Si:H layer and the n⁺-layer are etched by RIE method to separate therespective elements. In such a manner, the photoelectric conversionelement 601, the switching TFT 602, other wirings (606, 607, 609), andcontact hole parts 610 are formed. Incidentally, it is also possible toform an electron injection inhibiting layer by changing the p⁺-layer,which is a hole injection inhibiting layer, to an n⁺-layer. That is, thephotoelectric conversion element comprises an insulating film whichprevents both of the holes (the second carrier) and the electrons (thefirst carrier) from passing through, and an injection inhibiting layerfor inhibiting either one of the first and the second carriers frompassing through.

Incidentally, FIG. 6 shows only elements for 4 pixels; however, elementsfor a large number of pixels are simultaneously formed on the insulatingsubstrate 603. Finally, in order to improve the moisture resistance, therespective elements and wirings are coated with a passivation film(protective film) 615 of SiN_(x).

As described above, the photoelectric conversion device of thisembodiment is produced only by depositing the first metal thin filmlayer, the a-SiNx layer, the a-Si:H layer, the n⁺-layer and the secondmetal thin film layer on a whole plane, respectively, and etching therespective layers to commonly and simultaneously form the photoelectricconversion element, the switching TFT and the wirings.

In FIG. 7, a phosphor may be formed by directly depositing CsI on theprotective film 615, or by, after GOS is formed in a sheet-like state ina separate process, sticking it using an adhesive.

By employing the above described processes using an amorphous siliconsemiconductor as a main material, photoelectric conversion elements,switching elements, wiring for gate operation, and matrix signal wiringscan be simultaneously formed on the same substrate and a large surfacearea photoelectric conversion circuit part can easily and economicallybe provided.

FIG. 8 is a two-dimensional circuit diagram of the photoelectricconversion device illustrated in FIG. 1. In this circuit, only elementsequivalent to 3×3=9 pixels are illustrated in order to simplifydescription. In the figure, the reference numeral 801 denotes aphotoelectric conversion circuit part, 802 a shift register (SR1), 803 ashift register (SR2), 804 an operation amplifier, 805 an A/D conversioncircuit, 806A and 806B are d.c. power sources, 806I a diode, 807 acircuit part for reading-out, and 808 a photoelectric conversionelement.

The plan view and the cross-sectional view of the photoelectricconversion elements, the switching elements (TFT) and the like in FIG. 8are the same as those shown in FIG. 6 and FIG. 7. A photoelectricconversion element has the same layer structure as that of the switchingelement and is composed as an MIS type capacitor. Incidentally, for thepurpose of entering light rays in it, it is different from the normalMIS type capacitor in the point that an n⁺-layer is used as an upperpart electrode of the photoelectric conversion element. Thephotoelectric conversion element is a capacitor element as well and thesignal charge generated by photoelectric conversion is accumulated inthe capacity of itself.

Next, the description will be given regarding a method for carrying outoperation such as accumulation of the charge of photoelectricconversion, transmission through the TFT, signal reading out, aftercompletion of reset of a photoelectric conversion element, which is acapacitor, by using a bias circuit installed in the outer side, in thisembodiment shown in FIGS. 1 to 8. Further, the reset operation of theabove described photoelectric conversion element will be called as“refresh” hereafter. Incidentally, in FIG. 8, (S1-1) to (S3-3) are theabove described photoelectric conversion elements, and “G” electrodes ofthe photoelectric conversion elements are the first metal thin filmlayer in FIG. 6, and “D” electrodes are the second metal thin filmlayer. Incidentally, as described above, the “D” electrodes as well asthe n⁺-layer function as electrodes in the photoelectric conversionelements (S1-1) to (S3-3).

Next, the device operation of a photoelectric conversion element as asingle body will be described.

FIG. 9A to FIG. 9C show the energy band diagrams for illustrating thedevice operation of the photoelectric conversion element as a singlebody.

FIG. 9A and FIG. 9B illustrate the operation states in the refreshingmode and the photoelectric conversion mode, respectively, in thisembodiment and show the states in the film thickness direction of therespective layers shown in FIG. 7.

The reference symbol M1 denotes the lower part electrode (the Gelectrode) of a first metal thin film layer (Cr). The a-SiN_(x) layer isan insulating layer for inhibiting both of electrons and holes frompassing through and is necessary to be thick enough not to cause thetunnel effect and is set to be 50 nm or thicker. The a-Si layer is aphotoelectric conversion layer formed as an i-layer of an intrinsicsemiconductor. The n⁺-layer is an injection inhibiting layer of ann-type a-Si layer formed so as to inhibit injection of holes to the a-Silayer. Further, the reference symbol M2 denotes the upper part electrode(the D electrode) of a second metal thin film layer (Al).

Although the D electrode does not completely cover the n⁺-layer in thisembodiment, since the electrons are made to be freely transmittedbetween the D electrode and the n⁺-layer, the D electrode and then⁺-layer are always kept at the same potential and in the followingdescription that is presumed.

The photoelectric conversion element of this embodiment is provided withtwo types of modes, the refreshing mode and the photoelectric conversionmode, by the voltage application methods to the D electrode and the Gelectrode.

In FIG. 9A (refresh mode), negative potential is applied to the Delectrode in relation to the G electrode, and holes denoted by a solidblack circle (o) in an i-layer are led to the D electrode by an electricfield. Simultaneously, electrons denoted by an open circle (o) areinjected in the i-layer. At this time, a part of the holes and a part ofthe electrons are reconnected at n⁺-layer and i-layer, respectively, anddisappear. If such a state continues for a long enough time, the holesin the i-layer are swept out from the i-layer.

In order to convert the state (refreshing mode) shown in FIG. 9A to thestate (photoelectric conversion mode) shown in FIG. 9B, positivepotential is applied to the D electrode in relation to the G electrode.Consequently, electrons in the i-layer are led to the D electrode atonce. However, holes are not led to the i-layer since the n⁺-layer worksas an injection inhibiting layer. In such a state, when light rays enterthe i-layer, the light rays are absorbed and electron-hole pairs aregenerated. The electrons are led to the D electrode by an electric fieldand the holes move in the i-layer and reach the interface between thei-layer and the a-SiN_(x) insulating layer. However, the holes cannotmove to the insulating layer, and are accumulated in the i-layer. Theelectrons move to the D electrode and holes move to the interface withthe insulating layer in the i-layer, so that current flows from the Gelectrode in order to keep the electrically neutral state in thephotoelectric conversion element. The electric current corresponds tothe electron-hole pairs and is proportional to the incident light rays.

When the operation state is changed again to the state of FIG. 9A whichis a refreshing mode after keeping the state of FIG. 9B which is thephotoelectric conversion mode, the holes accumulated in the i-layer areled to the D electrode as described above and simultaneously the currentflows corresponding to the holes. The quantity of the holes correspondsto the total quantity of the light rays entering during thephotoelectric conversion mode period. At that time, although electriccurrent corresponds to the quantity of electrons injected to thei-layer, the quantity is approximately constant and therefore thedetection may be carried out by subtracting the current by that extent.In other words, in this embodiment, the photoelectric conversion elementoutputs a quantity of incident light rays at real time and at the sametime detects the total quantity of light rays which enter thephotoelectric conversion element during a certain period.

However, in the case where the period of the photoelectric conversionmode is long or the illuminance of the incident light rays is intensebecause of some reasons, sometimes no current flows in spite of enteringof the light rays. The cause for that is that, as shown in FIG. 9C, alarge number of holes is accumulated in the i-layer and the electricfield in the i-layer is reduced due to the holes, and the generatedelectrons are thus not led and subsequently re-coupled with the holes inthe i-layer. When the incident light state is changed in such a state,electric current sometimes flows unsteadily; however, by changing to therefreshing mode again, the holes in the i-layer are swept and in thenext photoelectric conversion mode, electric current in proportion tothe light rays can flow again.

Further, in the above described description, when the holes are swept inthe i-layer in the refreshing mode, it is ideal to sweep out all of theholes; however, an effect can be obtained even by sweeping only a partof the holes, and electric current equal to that in the case of entirelysweeping the holes can be obtained.

In other words, it is sufficient that the state at the time of thedetection in the next photoelectric conversion mode is not the stateshown in FIG. 9C, and the potential of the D electrode in relation tothe G electrode in the refreshing mode and the period of the refreshingmode and the properties of the injection inhibiting layer of then⁺-layer may be determined so as to satisfy that. Further, in therefreshing mode, injection of the electrons in the i-layer is adispensable condition and the potential of the D electrode in relationto the G electrode is not necessarily limited to be negative. This isbecause in the case where a large number of holes is accumulated in thei-layer, even if the potential of the D electrode in relation to the Gelectrode is a positive potential, the electric field in the i-layer isso generated as to lead the holes to the D electrode. Further, in thesame manner, the properties of the injection inhibiting layer of then⁺-layer are not necessary to be able to inject electrons to thei-layer.

Next, the operation of the photoelectric conversion device of thisembodiment will be described according t6 the above described FIG. 8 andFIG. 10.

FIG. 10 is a timing chart showing the operation of the photoelectricconversion device of FIG. 8.

In FIG. 10, the control signal VSC is for applying two types of bias tothe bias line REF of a photoelectric conversion element, that is, the Delectrode of the photoelectric conversion element. The D electrode is atVREF (V) when VSC is “Hi” and at VS (V) when VSC is “Lo”. The referencenumerals 106A and 106B denote d.c. power sources and they are a powersource VS(V) for reading-out and a power source VREF (V) for refreshing,respectively.

At first, the operation during the refreshing period will be described.

The signals of the shift resistor 102 are all put in the “Hi” state toput the CRES signals of the circuit part for reading-out in the “Hi”state. Subsequently, all of the TFT (T1-1 to T3-3) for switching areelectrically communicated and the switching elements RES1 to RES3 in thecircuit for reading-out are also electrically communicated and the Gelectrodes of all of the photoelectric conversion elements are kept atGND potential. When the control signal VSC becomes “Hi”, the Delectrodes of all of the photoelectric conversion elements are put inbiased state (at negative potential) by the power source VREF forrefreshing. Consequently, all of the photoelectric conversion elements(S1-1) to (S3-3) are operated in the refreshing mode.

Next, the photoelectric conversion period will be described.

When the control signal VSC is switched to “Lo” state, the D electrodesof all of the photoelectric conversion elements are put in biased state(at positive potential) by the power source VS for reading-out.Subsequently, the photoelectric conversion elements are put inphotoelectric conversion mode. In such a state, the entire signals ofthe shift registers 102 are put in “Lo” state and the CRES signals ofthe circuit part for reading-out are put in “Lo” state. Consequently,all of the TFT (T1-1 to T3-3) for switching are turned off and theswitching elements RES1 to RES3 in the circuit for reading-out are alsoturned off and although the G electrodes of all of the photoelectricconversion elements are put in the open state in terms of d.c. current,the potential can be maintained since the photoelectric conversionelements work also as capacitors.

However, at that time, since no light rays enter the photoelectricconversion elements, no electric charge is generated. In other words, nocurrent flows. In such a state, the light source is turned on by pulses(by a.c. current), light rays are radiated to the respectivephotoelectric conversion elements and so-called photocurrent flows.Regarding the light source, it is not particularly shown in FIG. 8, butin the case of a copying machine, for example, a fluorescent lamp, LED,a halogen lamp, or the like are employed. In the case of an x-rayimaging apparatus, it is of course an x-ray source, and a scintillatorwhich becomes a wavelength converter for x-ray-visible light conversionmay be employed. Further, semiconductors which are directly sensitive tothe radiation, such as GaAs and a-Se, may be used. The photocurrentflowing by the light rays is accumulated in the form of electric chargein the respective photoelectric conversion elements and maintained evenafter the light source is turned off.

Regarding the reading-out period, the description is omitted since it isthe same as described above.

After the refreshing period, the photoconversion period and the read-outperiod, one image can be obtained, and in the case of obtaining aplurality of images like a motion image, the above described operationmay be repeated. In this embodiment, since the D electrodes of thephotoelectric conversion elements are connected in common and controlledto be at the potential of the power source VREF for refreshing and atthe potential of the power source VS for reading-out by controlling thecommon wiring by the control signals VSC, all of the photoelectricconversion elements can simultaneously be switched to the refreshingmode and the photoelectric conversion mode. Therefore, without requiringcomplicated control, light output can be obtained with one TFT for onepixel.

In this embodiment, it is made possible to shorten the time taken tolower the dark current by lighting the second light sources installed inthe outer casing during the non-reading-out period. Further, especiallyin a radiation detection apparatus, the exposure duration of theradiation source is better to be shorter and separate installation ofthe second light sources in such a manner is effective to shorten thetime taken to lower the dark current without prolonging the exposureduration of the radiation source and therefore it is preferable toemploy the second light sources.

(Embodiment 2)

FIG. 11 is a cross-sectional view showing Embodiment 2 of aphotoelectric conversion device according to the present invention. InFIG. 11, the reference numeral 1101 denotes an x-ray source, 1102 anobject body to be read out, 1103 a chassis, 1104 a phosphor, 1105 aphotoelectric conversion element, 1106 an insulating substrate, 1107 aprotective layer, 1108 an LED, and 1109 is a light guide plate.

The different point from the photoelectric conversion device of theEmbodiment 1 illustrated in FIG. 1, is that the light guide plate 1109is installed under the photoelectric conversion substrate (theinsulating substrate 1106) and LED 1108 as a second light sourceprovided in the outer casing is arranged on the side face of the lightguide plate 1109. The material for the light guide plate to be used is atransparent material such as acrylic resin, glass or the like whoserefractivity is different from that of air.

FIG. 11 is a cross-sectional view showing the structure of thephotoelectric conversion device, and photoelectric conversion elementsare arranged in a two-dimensional state in the depth direction of thesheet face of FIG. 11. The LED is also arranged in a one-dimensionalstate in the depth direction of the sheet face of FIG. 11. The lightrays coming from the side face of the light guide plate 1109 proceed tothe inside of the light guide plate. At that time, the light raysproceeding at an angle more acute than the critical angle determined bythe refractivity of the light guide plate 1109 and the refractivity ofthe ambient refractivity are fully reflected in the light guide plateinterface and further proceed to the inside. On the other hand, thelight rays proceeding at an angle more obtuse than the critical angleare partially refracted and led to the photoelectric conversionsubstrate side. The radiation of the latter light rays at the time ofnon-reading-out can lower the dark current within a short time.

Although the upper face and the lower face of the light guide plate 1109shown in FIG. 11 are drawn like planes, surface roughening processingcan improve the diffusion property and the light rays coming out of thephotoelectric conversion substrate from the light guide plate areincreased. The light rays coming out of the insulating substrate sidepenetrate the side faces of the photoelectric conversion elements 1105,are reflected by the phosphor 1104 faces and reach the light-receivingfaces of photoelectric conversion elements 1105. The photoelectricconversion device of this embodiment is made capable of shortening thewaiting time without requiring installation of a second light sourcesuch as a large quantity of LEDs and without increasing the powerconsumption.

(Embodiment 3)

FIG. 12 is a cross-sectional view showing Embodiment 3 of aphotoelectric conversion device according to the present invention. Inthe figure, the reference numeral 1201 denotes an x-ray source, 1202 anobject body to be read out, 1203 a chassis, 1204 a phosphor, 1205 aphotoelectric conversion element, 1206 an insulating substrate workingalso as a light guide plate, 1207 a protective layer, and 1208 an LED.

In this embodiment, the insulating substrate in which the photoelectricconversion elements 1205 are arranged is used also as a light guideplate. The material for the insulating substrate working also as thelight guide plate 1206 is a transparent material such as acrylic resin,glass or the like whose refractivity is different from that of air. FIG.12 is a cross-sectional view showing the structure of the photoelectricconversion device and photoelectric conversion elements 1205 arearranged in a two-dimensional state in the depth direction of the sheetface of FIG. 12. As the second light source installed in the outercasing, the LED 1208 is also arranged in a one-dimensional state in thedepth direction of the sheet face of FIG. 12.

In FIG. 12, the light rays coming from the side face of the insulatingsubstrate also working as a light guide plate 1206 proceed to theinside. At that time, the light rays proceeding at an angle more acutethan the critical angle determined by the refractivity of the insulatingsubstrate also working as a light guide plate 1206 and the refractivityof the ambient refractivity are fully reflected in the lower face of theinsulating substrate also working as a light guide plate 1206 andfurther proceed to the inside. On the other hand, the light raysproceeding at an angle more obtuse than the critical angle are partiallyrefracted and led to the photoelectric conversion substrate side. If thelight rays are radiated to the photoelectric conversion element at thetime of non-reading-out, the dark current can be lowered within a shorttime. Although the lower face of the insulating substrate also workingas a light guide plate 1206 shown in FIG. 12 may be a flat face, if itis surface-roughened, the diffusion property is increased and the lightrays coming to the side of the phosphor 1204 from the side of theinsulating substrate also working as a light guide plate 1206 areincreased. The light rays coming to the side of the phosphor 1204penetrate the side faces of the photoelectric conversion elements 1205,are reflected by the phosphor faces and reach the light-receiving facesof photoelectric conversion elements 1205. On the other hand, in theupper face of the insulating substrate also working as a light guideplate 1206, the light rays coming into collision with the first metalthin film layer of the photoelectric conversion elements 1205 (and theswitching elements) are reflected at a high ratio. Also, the light rayscoming into collision with the protective layer 1207 other than thefirst metal thin film layer are reflected or refracted depending on thelight proceeding conditions determined by the refractivity of theprotective layer 1207 and the refractivity of the insulating substratealso working as a light guide plate 1206.

The photoelectric conversion device of this embodiment is made capableof shortening the waiting time without requiring installation of thesecond light sources such as a large quantity of LEDs and withoutincreasing the power consumption. Further, the photoelectric conversiondevice can be light in weight and compact in size since the insulatingsubstrate is used also as a light guide plate.

(Embodiment 4)

FIG. 13 is a cross-sectional view showing Embodiment 4 of aphotoelectric conversion device according to the present invention. InFIG. 13, the reference numeral 1301 denotes an x-ray source, 1302 anobject body to be read out, 1303 a chassis, 1304 a phosphor, 1305 aphotoelectric conversion element, 1306 an insulating substrate workingalso as a light guide plate, and 1307 a protective layer.

In this embodiment, a plurality of light sources are not particularlyinstalled and external light is used in place of a light source in theouter casing. The outer casing is opened when the external light istaken in the light guide plate side and closed during the time otherthan that. The opening and closing may automatically be controlled by amotor. Since no space is required for installation of any light sourcein the outer casing, the apparatus can be miniaturized. Further, byproperly selecting the motor, the electric power consumption can also bereduced. This embodiment is especially effective in the case where theexternal light quantity is intense.

(Embodiment 5)

FIG. 14 is a cross-sectional view showing Embodiment 5 of aphotoelectric conversion device according to the present invention. InFIG. 14, the reference numeral 1401 denotes an original document, 1402 aphotoelectric conversion element, 1403 an insulating substrate, 1404 aprotective layer, 1405 a chassis, and 1406 an LED.

The photoelectric conversion device according to this embodiment is amode adapted to a copier or a facsimile reading an original document.

FIG. 14 is a cross-sectional view showing the structure of thephotoelectric conversion device, and photoelectric conversion elements1402 and LED 1406 are arranged in a two-dimensional state in the depthdirection of the sheet face of FIG. 14. Further, although they are notshown in FIG. 1 of Embodiment 1, the photoelectric conversion elements1402 and switching elements may be arranged in pairs on the insulatingsubstrate 1403.

The light rays (visible light rays) emitted out of the LED 1406 arrangedunder the insulating substrate 1403 are transmitted through theinsulating substrate 1403, pass the side faces of the photoelectricconversion elements 1402, and reach the original document 1401, which isan object to be read out. Corresponding to the densities of the lettersand the images drawn on the surface of the original document, the lightrays are reflected by the original document face and radiated to thelight-receiving faces of the photoelectric conversion elements 1402.

The LEDs are turned on during both the reading-out periods and thenon-reading-out periods. The lighting of the LED 1406 during thereading-out period is to read out the data of the original document byphotoelectric conversion elements 1402. By lighting the LED duringimage-pickup and during the non-reading-out period, the dark current canbe decreased during the reading-out period. Regarding the lighting ofthe LED during the non-reading-out period, the original document 1401may be put or may not be put on the upper part of the photoelectricconversion elements and it is sufficient for some quantity of light raysto reach the light-receiving faces of the photoelectric conversionelements 1402.

Depending on the raw materials of the original document itself or theink, the original document has different reflective properties to lightrays from the LED and any is acceptable unless it completely absorbslight rays and it is sufficient for the original document to reflectseveral % of light rays so as to reach the photoelectric conversionelements. Since there practically exist light rays coming from thediagonal direction, if components reflected by the mirror face of theoriginal document face are included in the reflected light rays, theoriginal document can never entirely absorb light rays. Further, in thecase where no original document exists, the components of the light raysin the perpendicular direction from the LED do not reach thephotoelectric conversion elements at a high ratio and since therefractivity of the protective layer and the refractivity of the ambientair differ from each other, the light rays from the diagonal directionfrom the LED and the light rays scattered by the edge parts of the metalthin film layers of the photoelectric conversion elements and theswitching elements and emitted in the diagonal direction are partlyreflected to the photoelectric conversion element side by the protectivelayer interface.

(Embodiment 6)

FIG. 15 is a circuit diagram of a photoelectric conversion element asone pixel showing Embodiment 6 according to the present invention.

A photoelectric conversion element 1503 shows a PIN type photo diode,and usable as a material is possibly amorphous silicon, crystallinesilicon, or the like.

The cathode side of the diode of a photoelectric conversion element 1503is connected with an SW1 and the anode side is connected with anammeter. The other side of the SW1 is made switchable to be connectedeither with a power source (Vs) for applying bias to the photoelectricconversion element or a zero bias (GND). The x-rays radiated from anx-ray source 1501, which is a first light source, are radiated to anobject body to be inspected (a patient in the case of a hospital), whichis not shown in FIG. 15, and the x-rays transmitted through the objectcome into collision with a phosphor 1502 which is an x-ray wavelengthconverter. The x-rays are converted to visible light rays by thephosphor 1502. The visible light rays from the phosphor 1502 areradiated to a photoelectric conversion element 503.

Since the circuit diagram of the photoelectric conversion element ofthis embodiment shown in FIG. 15 shows a circuit diagram only for onepixel, the positioning correlation between the photoelectric conversionelements and the phosphor is therefore not illustrated. However,similarly as in Embodiment 1 illustrated in FIG. 1, the image resolutionproperty is improved by practically closely attaching both of them toeach other. On the other hand, the visible light rays from the LED lightsource 1504, which is a second light source, are radiated to thephotoelectric conversion elements 1503 through another optical pathdifferent from that for the x-rays. SW2 and SW3 are switches for turningon the x-ray source 1501 and the LED light source 1504, respectively.

FIG. 16 is a timing chart of operation in the circuit of this embodimentshown in FIG. 15 and shows the x-ray source, the LED light source, biasof the photoelectric conversion element, and the output of thephotoelectric conversion elements. In FIG. 18, the x-ray source and theLED are not to be lighted in order to show the state of dark output (thedark current) of the photoelectric conversion element.

In the FIG. 18, when bias is applied to the photoelectric conversionelement, the dark current flows in the photoelectric conversion element.It is preferable for the dark current to be ideally zero; however, it isdifficult to be zero. Further, constant electric current does not flowsimultaneously with the time when the electric power source is turnedon, but the dark current is high immediately after the turning-on andgradually decays with the lapse of time.

Generally even in the case where the photoelectric conversion elementsare fabricated using the PIN photodiode containing mainly an amorphoussilicon semiconductor as a material, the dark current flows as describedabove.

Additionally, the blocking properties of a p-layer and an n-layer arenot perfect and it is supposed that components for dark current areincreased owing to the carriers flowing in the inside of an i-layer fromthe outside.

Further, in the case of using a crystal type PIN-type photodiode withoutusing an amorphous semiconductor film, it is said that the trap levelsare not so many as compared with those in the case of using an amorphoussemiconductor, although it depends on the process conditions and theapparatus to be fabricated. However, many crystal lattices aremismatched in the interface part between the p-layer and the i-layer andin the interface part between the i-layer and the n-layer, the traplevels are not zero, and there is a tendency of the output of thephotoelectric conversion elements to be as shown in FIG. 16.

A signal with a high S/N ratio can be obtained by waiting until the darkoutput (dark current) of the photoelectric conversion elements issufficiently decayed. However, it takes as long as several seconds toseveral ten seconds to decay the dark current to an aimed dark outputlevel. In this case, for example, when the photoelectric conversionelements are employed for an x-ray imaging apparatus to be used in ahospital, the following procedure is required: a patient is guided to aphotographing chamber, the photoelectric conversion elements are turnedon, and after waiting for several to several ten seconds, the patient issubjected to x-ray exposure. Although it is better to turn on theelectric power source for the photoelectric conversion elements before apatient comes in the photographing chamber, in that case, deterioration(property change, corrosion, or the like) of the photoelectricconversion elements is accelerated making it difficult to provide anapparatus with a long life.

FIG. 17 is a timing chart of the operation in the circuit of thisembodiment illustrated in FIG. 15 and shows the case of lighting the LEDlight source after the electric power source of the photoelectricconversion elements is turned on.

By turning on the LED, photocurrent flows in the photodiode and finally,simultaneously with the time when the LED is turned off, thephotocurrent is stopped. At that time, the dark current after theturning off of the LED is stabilized with the lapse of time or in somecases lowered as compared with that in the case where the LED is notturned on (in the timing chart of FIG. 16). That is because the innerstate (especially in the interface part) of a semiconductor layer isstabilized by excess carriers generated in the inside of thesemiconductor layer by the photoenergy radiated by the LED, and eitherelectrons or holes are released by the light radiation. If x-rays areradiated in such a low dark current state, signals with a high S/N ratiocan be obtained.

In other words, an x-ray image with a high S/N ratio can be obtainedwithout taking a long waiting time by lowering the dark current byradiating LED light before x-ray photography.

FIG. 18 is a timing chart showing the output situation of thephotoelectric conversion elements when x-rays are turned on after theLED is turned on.

The LED is previously turned on in order to lower the dark current ofthe photoelectric conversion elements at the time when x-ray exposure isto be carried out within a short time. The photocurrent flowing at thattime has nothing to do with the reading out of the image data. Theperiod during which the LED is turned on is called as thenon-reading-out period. On the other hand, x-rays are radiated only forreading-out the internal data of a patient. The period during whichx-rays are radiated is called as the reading-out period. The light raysof the LED (the second light source) are radiated during thenon-reading-out period, and x-rays (the first light source) are radiatedduring the reading-out period. The duration of the non-reading-outperiod and the reading-out period or the radiation duration of the LEDmay be determined depending on the properties of the dark output (thedark current) of the photoelectric conversion elements and the S/N ratiorequired for the photoelectric conversion device.

(Embodiment 7)

FIG. 19 is a block diagram of a photoelectric conversion device ofEmbodiment 7 according to the present invention. In the block diagram ofFIG. 19, illustrated is the schematic diagram of an image processingsystem using an x-ray imaging apparatus to be employed in a hospital. InFIG. 19, the reference numeral 1901 denotes an x-ray source, 1902 apatient, 1903 a photoelectric conversion element, 1904 an x-ray-visiblelight converting phosphor, 1905 a protective layer, 1906 a substrate,1907 an LED, 1908 control means, 1909 a timing generation apparatus, and1910 a plurality of driving signals.

In FIG. 19, radiation, for example, x-rays radiated from an x-ray sourceare radiated to the patient 1902 and the x-rays transmitted through thepatient reach the x-ray imaging (image-pickup) apparatus. The x-rays areconverted to visible light rays by the phosphor which is a wavelengthconverter, and the visible light rays are radiated to the photoelectricconversion elements 1903. The visible light rays contain the image dataof the patient 1902. The photoelectric conversion elements 1903 and thewavelength converter are practically closely attached to each other andin FIG. 19, they are closely attached through the thin protective film1905. Further, the photoelectric conversion elements 1903 are installedon the substrate 1906. A light source is installed on a side opposite tothe light-receiving face side of the photoelectric conversion elements1903 on the substrate 1906. In this case, the LED is used as the lightsource. The light rays from the LED 1907 are transmitted through thesubstrate 1906 and reflected by the wavelength converter and then reachthe photoelectric conversion elements 1903.

The radiation (switching on) of x-rays and lighting (switching on) ofthe LED light source and switching off are controlled by control means.

In FIG. 19, although only the photoelectric conversion elements areillustrated, a switching element may be installed just like the2-dimensional circuit diagram as shown in FIG. 8. Further, in FIG. 19,although only the photoelectric conversion elements installed on thesubstrate are illustrated, the photoelectric conversion circuit part 801and the circuit part for reading-out 807 as shown in FIG. 8 areinstalled as well. The photoelectric conversion circuit 801 and thecircuit part for reading-out 807 are operated by signals based on thetiming chart shown in FIG. 10. These signals are VSC, REF, CRES, G1, G2,G3, SMPL, Sr1, Sr2, Sr3 or the like. They are outputted by a timinggeneration apparatus and inputted to the photoelectric conversion device(801 and 807 shown in FIG. 8). In other words, the signals from thetiming generation apparatus operate the photoelectric conversion device.As shown in FIG. 19, the timing generation circuit is controlled(ON/OFF) by the control means. As an example of constitution of thecontrol means, a computer is available. The control means independentlycontrols the x-ray source, the photoelectric conversion device, and theLED which is a second light source, and if a computer is employed forthe control means, the control method can be programmed using software.That is, the handling convenience can be improved and consequently, theadded value to the x-ray imaging apparatus to be used in a hospital isincreased.

Further, also possible is a method which comprises installing the A/Dconversion circuit part 805 shown in FIG. 8, which is not shown in FIG.19, in the periphery of the photoelectric conversion circuit part 801and the circuit part for reading-out 807, and storing the digital dataof the A/D conversion circuit part 805 in the memory of the computer(the control means).

1.-19. (canceled)
 20. A radiation detection apparatus comprising: aplurality of photoelectric conversion elements arranged on a surface ofa substrate; and an outer casing that houses at least the photoelectricconversion elements, wherein the outer casing has a mechanism whichopens when light is taken from an outside of the outer casing and whichcloses when light is not taken from the outside of the outer casing. 21.The radiation detection apparatus according to claim 20, furthercomprising a light guide plate.
 22. The radiation detection apparatusaccording to claim 21, wherein the mechanism provided in the outercasing is arranged on the side face of the light guide plate.
 23. Theradiation detection apparatus according to claim 20, wherein thephotoelectric conversion elements are arranged on an insulatingsubstrate, and the insulating substrate is also used as a light guideplate.
 24. The radiation detection apparatus according to claim 20,further comprising a wavelength converter for converting radiationemitted from a radiation source onto the surface of the substrate intolight, and wherein the mechanism is arranged in the outer casing on asurface side thereof opposite to the surface of the substrate.
 25. Theradiation detection apparatus according to claim 20, wherein thephotoelectric conversion elements each include a first electrode layerand a second electrode layer, an insulating layer formed between thefirst and second electrode layers for inhibiting a first type ofcarriers from passing through the layer, a semiconductor layer, and aninjection blocking layer for inhibiting the first type of carriers frombeing injected into the semiconductor layer, and the light source emitslight with a wavelength for generating carriers which are photo-absorbedin the semiconductor layer and are retained on an interface of theinsulating layer.
 26. An image data processing system, comprising: theradiation detection apparatus according to claim 20; a radiation source;and control means for independently controlling the radiation source,the light source and the photoelectric conversion device.